Multiple plane holographic projection using diamond turned holograms

摘要

Diffractive optical elements (DOE) are widely used for the projection of desired intensity distributions, e.g. in security or automotive applications. Diamond turning based on a nano Fast Tool Servo offers short fabrication times and low costs for small quantities. The main properties of diamond turned metal DOEs for the holographic projection are their small pixel size down to 1 μm in feed direction, high reflectivity and mechanical and thermal stability. Currently, existing methods are limited to the projection of intensity distributions in only one plane. However, more than one projection plane is highly desirable for applications as automotive lighting, laser material processing and security features. In this contribution, we introduce an approach for the optical design of diamond turned holograms (DTH) for the holographic projection of arbitrary intensity distributions in multiple reconstruction planes in the Fresnel domain. The design problem is related to the spiral path of the diamond cutting tool and to find a set of N wavefields which generate intensity distributions in different distances d_n. For calculating the cutting depth profile of the DTH a combination of the Gerchberg-Saxton-Algorithm with an iterative phase retrieval algorithm is applied. The use of Fresnel propagation in the algorithm allows the generation of intensity distributions in large projection areas with low computational effort. We present the theory as well as the experimental verification of this new approach.